Neurobiology of Language -

The ‘ignored’ speech is not ignored

Most listening environments are filled with various types of background noise, and the most troubling noise is often the competing speech heard in the public spaces, like restaurants, bus stations, and classrooms. The comprehension of the target speech can be degraded by the other interfering signals. Given the plentiful features encoded in the background sounds, masking could occur at different levels of the speech processing hierarchy. A recent published study by Bohan Dai and colleagues tried to disentangle the effects related to acoustic processing from those related to linguistic analysis.

An A-B-A training paradigm was used to manipulate the linguistic component of the distractor without changing its acoustic component. The experiment consisted of three phases. In the first and third phases of the experiment, participants performed a dichotic listening cocktail-party task(A), in between the two dichotic listening tasks participants were trained to understand 4-band noise-vocoded speech(B). Crucially, the noise-vocoded speech was initially poorly intelligible but could be understood after training. Hence, before and after training, the noise-vocoded speech would have the same acoustic information but not carry the same linguistic information.

A stronger masking effect of the interfering signal was observed, which was contributed by the incremental linguistic information through training. Noise-vocoded speech interfered more with target speech comprehension after training (i.e., when intelligible) than before training (i.e., when unintelligible) at −3 dB SNR. This study provides insights about auditory scene analysis, where the ignored signal is not ignored, but even partly processed at higher linguistic levels. A magnetoencephalography study is currently being performed, to specifically investigate the underlying neural mechanisms.

What is the neurobiological infrastructure for the uniquely human capacity for language? The focus of the Neurobiology of Language Department is on the study of language production, language comprehension, and language acquisition from a cognitive neuroscience perspective. Read more...